There is a group of electrical receptacles which can be referred to as "protective" receptacles because some measure has been taken in the construction to protect children and others from harm if they should intentionally or inadvertently insert or attempt to insert an electrically conductive article into the electrically energized portions of the receptacle. Conventional receptacles, of course, have a nonconductive face portion with openings to receive plug blades. In normal use, the blades pass through the nonconductive space and are received by conductive female spring elements which are connected to line voltage. A child inserting, for example, a paper clip or the conductive portion of a toy into the energized spring elements can be seriously injured.
To avoid this danger, several different kinds of safety receptacles have been designed, and these fall into two general categories. One category is those receptacles which have internal switches and movable members between the faceplate and the female spring elements to operate the switches only when a predetermined number, type, or shape of blade elements is inserted concurrently. The purpose of devices of this type is to avoid energization of the internal conductive portions of the receptacle unless predetermined conditions exist, these conditions being those which would normally be present only when the appropriate plug or the like is inserted. Generally, insertion of an article is not inhibited; rather, the existence of voltage in the receptacle is controlled. Examples of devices of this type are found in U.S. Pat. Nos. 4,271,337, Barkas, and 2,500,474, Sperrazza, and the references cited therein.
Another category of protective receptacles can be referred to as "shuttered" receptacles, the principle of operation of this type being that insertion of anything other than the blades of an appropriate plug is inhibited by elements provided between the faceplate and the conductive elements. There is no effort to control the electrical energization of internal components; rather, access to those conductive elements is prevented except under a defined set of circumstances.
An example of a device of this type is found in U.S. Pat. No. 4,379,607. Bowden, Jr., and the references cited therein also provide examples of both the shuttered and switched types of electrical receptacles. Bowden is of particular interest because two relatively slideable members are provided behind the slots in the faceplate and in front of the terminals within the receptacle housing. The two members are identical, each having a cam surface and a blocking portion, the cam surfaces being positioned so that each one is contacted by a blade and is caused to move so that its blocking member unblocks the slot for the other blade. Thus, when the two blades are concurrently inserted, they act against the two cam surfaces and unblock each other's passageways.
While this structure appears to be quite suitable for its intended purpose, and while it does have the advantage of permitting the use of shuttering in a grounded plug and receptacle, the design is such that it can only be used with plugs having parallel blades such as type 1-15 P and 5-15 P.
As is well known, however, plugs and receptacles used in the home as well as in offices and other circumstances at the present time include configurations such as 5-20 P, 6-20 P and others in which the blades are perpendicular to each other rather than being parallel. The receptacles, such as 5-20 R, are configured to be able to receive either the 5-15 P or 5-20 P plugs. The structure of Bowden is simply not usable with configurations of this type, nor are the other shuttered and switched structures of the prior art.